to block the addresses, but I think that only works for hosts, not senders.I tried using qq.com, @qq.com, *@qq.com, but the messages still keep coming through.I tried blocking the IP address of the servers that are connecting, but those are randomized also. Each 2 or 3 connections, the IP addresses are totally random, so blocking the IP address is pointless.

I have same problem on few zimbra servers. I use official zimbra instruction - blocking domain, but nothing.In main.cf nothing. In smtpd_sender_restrictions.cf exists %%contains VAR:zimbraMtaSmtpdSenderRestrictions check_sender_access lmdb:/opt/zimbra/conf/postfix_reject_sender%%